WEDNESDAY, Aug. 28 (HealthDay News) -- Mental and substance abuse disorders were the leading cause of nonfatal health issues around the world in 2010, researchers say.

These disorders were responsible for more of the global burden of deaths and illnesses than HIV/AIDS, tuberculosis or diabetes, according to the new findings from the Global Burden of Disease Study.

Meanwhile, a separate study revealed that opioid dependence causes the greatest health burden of all illicit drugs. Of the roughly 78,000 drug disorder deaths in 2010, 55 percent were believed to be the result of opioid dependence.

The studies appeared in the Aug. 29 issue of The Lancet.

In conducting the first study, researchers in the United States and Australia examined information from 187 countries on 20 mental and substance abuse disorders to determine the prevalence, premature death and nonfatal illness caused by these disorders. Mental and substance abuse disorders were responsible for nearly 23 percent of all disease burden worldwide.

Although substance abuse disorders were reported to have caused relatively few deaths in 2010, the researchers pointed out that this is because these deaths were attributed to the physical cause of death -- not the substance abuse itself.

For the purposes of the research, deaths resulting from suicide were classified as injuries. Meanwhile, deaths from illegal drugs are often classified as accidental poisonings, so the actual number of deaths resulting from drug abuse may be higher.

Although drug and alcohol dependence was more common among men, the study revealed that females aged 10 and up had a greater burden of death and disease from mental disorders than males. Only China, North Korea, Japan and Nigeria had burdens of death and disease from mental and substance abuse disorders that were significantly lower than the global average.

"Mental and substance use disorders are major contributors to the global burden of disease and their contribution is rising, especially in developing countries. Cost-effective interventions are available for most disorders but adequate financial and human resources are needed to deliver these interventions," study leader Harvey Whiteford, of the Queensland Centre for Medical Health Research at the University of Queensland in Australia, said in a journal news release.

"Despite the personal and economic costs, treatment rates for people with mental and substance use disorders are low, and even in developed countries, treatment is typically provided many years after the disorder begins," Whiteford pointed out.

"In all countries, stigma about mental and substance use disorders constrain the use of available resources as do inefficiencies in the distribution of funding and interventions. If the burden of mental and substance use disorders is to be reduced, mental health policy and services research will need to identify more effective ways to provide sustainable mental health services, especially in resource-constrained environments," he concluded.

A separate study also showed that opioid addiction, such as heroin, causes the greatest health burden of all illegal drugs. The study found that more than two-thirds of those who were dependent on drugs were men, mostly aged 20 to 29. Of these, 64 percent each were addicted to marijuana and amphetamines, and 70 percent each were dependent on opioids and cocaine.

The burden in the worst affected countries, primarily developed nations, such as the United States, the United Kingdom and Australia, was 20 times higher than in the least affected countries, the results showed.

Although marijuana is the most commonly used illegal drug, only 13 million people around the world are hooked on marijuana, the study authors noted. Meanwhile, 17.2 million were addicted to amphetamines and 15.5 million were addicted to opioids.

In addition, smoking and alcohol remain responsible for around 10 percent of the total death and illness burden worldwide.

The study's co-leader, Louisa Degenhardt, of the National Drug and Alcohol Research Centre at the University of New South Wales in Sydney, pointed out in the news release that the study "results clearly show that illicit drug use is an important contributor to the global disease burden, and we now have the first global picture of this cause of health loss."

Moreover, Degenhardt added, "much can be done to reduce this burden. Although we have fewer means of responding to some causes of burden, such as cocaine and amphetamine dependence, well-evaluated and effective interventions can substantially reduce two major causes of burden -- opioid dependence and injecting drug use."

In a commentary accompanying the studies, Michael Lynskey and John Strang, with the National Addiction Centre at King's College London, said that "the importance of this project in guiding policy cannot be overestimated."

They noted that the "relative lack of information about the prevalence of mental and drug use disorders, and the harms associated with these disorders, emphasizes the need not only for continued and ongoing efforts to refine the methods used in the current project but also for increased efforts to quantify both the prevalence of mental and drug use disorders and the risks posed by these conditions."